The present invention relates generally to methods and devices for voltage frequency transformation, and more specifically to such a device having additional digital or analog processing.
Transformation of a continuous signal to a discontinuous signal brings advantages with it for a number of applications. For this reason, voltage frequency transformers are used in the most varied fields of electrical technology and electronics. For example, for control of electric motors, the actual current or voltage values can be easily integrated into a digital control concept by transformation into a sequence of impulses proportional to the actual current or voltage value.
For inclusion of the acquisition of the actual voltage or current value, for example in the control concept of an electric motor, it is advantageous to digitalize the continuous signal at the location where it is acquired and to transmit it in the form of impulses with a varying impulse sequence frequency. Even when using analog control, it can be advantageous to use digital signals for signal transmission at first, and then to transform them back into a continuous signal, because of the fact that digital signals are less likely to be affected by interference.
Because of the small dimensions demanded in many applications, and the requirement for extremely fast and highly accurate digitalization of an input signal and with great frequency deviation at the lowest possible costs, it is not always possible to rely on conventional voltage frequency transformers available on the market.
International application PCT/DE 89/00197, discloses a method for voltage frequency transformation by which a fast and highly accurate voltage frequency transformer with a wide frequency range can be achieved. This method uses a conventional integrating frequencycontrolled oscillator, which gives off a highly accurate frequency signal (pulse sequence signal) by means of precise regulation. For this regulation, the output signal of the frequency-controlled oscillator is essentially transformed back into a constant voltage, via a precision monoflop which is clocked by a quartz oscillator, a precision switch and a low-pass filter, compared with the input voltage of the frequency-controlled oscillator and used for control of the latter.
The accuracy demanded for the frequency signal of the voltage-controlled oscillator--for example for the control of electric motors--lies at 0.5 per mil. At very high frequencies of the frequency signal (impulse duration approximately 100 ns), this accuracy can hardly be achieved. In addition, beat interference can occur in the formation of the precision impulses by the precision monoflop, resulting in inaccuracies in regulation.
The voltage frequency transformer described in the international application (PCT/DE 89/00197) allows a precise digital evaluation in a broad frequency range. However, to achieve the necessary accuracy for an analog evaluation, additional measures have to be taken at high frequencies. This increases the complexity of the voltage transformer.
The present invention is directed to the problem of developing a method and a device for voltage frequency transformation at great frequency deviation, using simple means.